The demand for improved indoor air quality (IAQ) has generated a need for gas phase filtration units capable of removing contaminants such as volatile organic compounds (VOCs), tobacco smoke, carbon monoxide, and formaldehyde. Strategies to remove these harmful contaminants include employing a packed bed or an adsorbent-entrapped filtration media such as microfibrous sorbent-supported media (MSSM). Through a wet-laid process, MSSM's sinter-locked matrix of micron sized fibers is able to entrap sorbent particles with diameters as low as 30 microns leading to better chemical removal efficiency and higher sorbent utilization than a traditional packed bed. The disadvantages of adsorbent-entrapped media are a high pressure drop generated by small, entrapped sorbent particles and a low saturation capacity due to the relatively thin thickness of the media. [Harris et. al, Wet Layup and Sintering of Metal-Containing Microfibrous Composites for Chemical Processing Opportunities, Composites Part A: Applied Science and Manufacturing 32(8): 1117-1126 (2001)]
New tactics for building more efficient gas phase filters needs to be researched in order to maximize the usefulness of adsorbent-entrapped media. Pleated and V-bank filters are two designs that are able to improve both pressure drop performance and overall capacity for filtration units made from these materials. By understanding the pressure drop limitations within these filtration systems, additional media and adsorbent material are able to be packaged into a unit to increase the contaminant removal capacity while maintaining an acceptable resistance.
The flow resistance of a filter is a critical design and operational parameter. A large pressure drop across the filter is able to overload the air handler unit and reduce air flow. More importantly, the pressure drop is directly related to the energy consumption of the filtration system. Energy consumption is able to account for 80% of the total expenses while labor and procurement cost account for the remaining 20%. [Arnold et al., Life-cycle costing of air filtration, ASHRAE Journal 47 (11):30-32 (2005)]
Numerous filter designs are commercially available, yet pleated filters are one of the more popular styles due to their unique performance benefits. A pleated filter uses a highly folded media to increase the available filtration area and extend the filter's useful life. The extra area also bestows the additional advantage of reducing the pressure drop and energy consumption of the filter. The resistance across a pleated filter fits a second order polynomial composed of a geometric (KgV2f) and media (KmVM) term.ΔPF=KgV2f+KmVM  (1)Empirical and CFD approaches have been attempted by [Chen et al., Filter Pleating Design for Cabin Air Filtration. Annual Index/Abstracts of SAE Technical Papers, Technical Paper 960944 (1996)], [Rivers and Murphy, Air Filter Performance Under Variable Air Volume Conditions, ASHRAE Transactions 106(2): 131-144 (2000)], [Caesar and Schroth, The Influence of Pleat Geometry on the Pressure Drop in Deep-Pleated Cassette Filters, Filtration and Separation 39(9):48-54 (2002)], [Del Fabbro et al., Air Flows and Pressure Drop Modeling for Different Pleated Industrial Filters, Filtration and Separation 39(1):34-40 (2002)], and [Tronville and Sala, Minimization of Resistance in Pleat-Media Air Filter Designs: Empirical and CFD approaches, HVAC & R Research 9(1):95-106 (2003)] to determine the constants. Although each method produces accurate results, the models are only applicable to the specific filters studied and lack predictive capabilities due to the heavy reliance on empirical data. The contributions of the pleat tips and filter housing, mentioned by [Raber, Pressure Drop Optimization and Dust Capacity Estimation for a Deep-Pleated Industrial Air Filter Using Small Sample Data, Filtration and Separation 19(6):508-511 (1982)], are often neglected from the models.